This invention relates to graphic imaging systems and more specifically character printers which are particularly useful in phototypesetters.
During the last 30 years, numerous so-called second generation phototypesetters have been marketed. These machines flash-illuminate characters positioned upon a whirling character disk or drum, and the resulting optical image is projected by a lens system upon a photosensitive film. The size of the characters are changed by means of moving zoom lenses or the like or by rotating a lens turret to position various lenses at the optical projection axis. The characters are sequentially recorded upon the photosensitive film by mechanically scanning such film which may be accomplished in various ways. The film carriage may be moved relative to the optical axis, the projection lenses may be moved relative to the film platen, the whirling character disk may be moved relative to the film platen, or various combinations of the foregoing may be employed to sequentially project the characters upon the film to form a line of characters. Generally, the projection lens carriage assemblies are relatively heavy and bulky, as is the drum or disk bearing the images of the characters to be projected. Also, changes in the fonts involve manual replacement of the character disks, or film strips mounted upon a drum. Additionally, the electromechanical stepping devices for producing the above mentioned scanning motions are also relatively bulky and cumbersome. The speed of second generation machines is limited by the output carriage escapement speed and by character access time determined by the rotational speed of the font disk.
So-called third generation phototypesetters were introduced in the 1960s, most of which utilize cathode ray tubes for generating the characters upon the face of the tube. These character images are thereafter optically projected upon the film. In contrast with the components of the second generation machines, the electron beam is inertialess and the binary character codes thus may actuate the beam at much higher speeds than those obtainable by the second generation machines. Inertialess laser generated light beams have also been employed rather than cathode ray tubes. Many font families may be generated by these machines since the character generating codes may be densely packed during recordation upon magnetic storage media, such as floppy disks. Also, the character size may be electronically changed by changing the length of the beam traces making up the character components (See FIG. 1 of Pat. No. 3,952,311).
The result of the foregoing is that these machines have higher speeds, and greater flexibility in the character shapes and sizes produced. However, the third generation machines are usually considerably more expensive than the second generation machines; in 1979, they typically sold for $40,000 on up. In contrast, second generation machines in 1979 have been marketed for around $10,000.
It is a principal object of the present invention to provide a fourth generation phototypesetter that can be marketed for around $10,000, and yet have the speed and flexiblity of third generation machines.
It is a further object of the invention to provide a phototypesetter that is relatively light in weight and compact, since the relatively bulky high mass components of the second generation phototypesetters have been eliminated.
It is yet a further object of the present invention to provide a radically new phototypesetter having a printing device which is very inexpensive and may be rapidly replaced to reduce maintenance costs. One approach useful in attaining the above stated objectives is the subject of my co-pending application entitled "LED-Fiber Optic Character Printer," no. 181,312, filed Aug. 25, 1980.
The present invention is somewhat similar to U.S. Pat. No. 4,096,486 of Pfeifer et al issued June 20, 1978. Pfeifer teaches the use of a matrix of LEDs which form a plurality of points on a relatively narrow strip of film which is driven under the stationary matrix. The light emitted by the LEDs is focussed by a plurality of lenses upon the moving film. In FIG. 2, Pfeifer teaches the skewing of the linear arrays of LEDs and lenses so that the resolution of the image is satisfactory despite the fact that LEDs themselves are relatively large. In other words, without the skewing, the relatively large dimensions of the LEDs would produce unsatisfactory resolutions of the images. The teachings of Pfeifer are impracticable in attaining the above stated objects of the invention which require very rapid production of lines of characters across the film perpendicular to the leading motion of the film, to record line after line of characters on the film. If one were to attempt to adapt the teachings of Pfeifer, a relatively heavy platen supporting photosensitive roll material would have to be driven in a direction perpendicular to the leading motion which provides the line by line scanning of sentences. Relatively heavy drive motors would be required to drive the platen bearing the film and the speed of operation would be limited by the inertia of the start-stop motion at the beginning and end of the line scan. Furthermore, the manufacturing cost of the above-mentioned heavy and accurately aligned platen drive system would be relatively high, and the use of the lens matrix of Pfeifer would limit the accuracy in the resolution of the images due to manufacturing and alignment tolerances. Another advantage of the present invention over the teaching of Pfeifer is the fact that Pfeifer must maintain precise optical geometry to assure proper focus whereas the present invention is essentially a contact printing process.